Receiving part for receiving a rod for coupling the rod to a bone anchoring element

ABSTRACT

A receiving part for receiving a rod for coupling the rod to a bone anchoring element includes a receiving part body including a first end and a second end, and having a substantially U-shaped recess at the first end forming a channel for receiving the rod, and an accommodation space for accommodating a head of the bone anchoring element, the accommodation space having an opening at the second end for introducing the head; and a pressure element arranged at least partially in the accommodation space, the pressure element including a first section having a second recess for receiving the rod, and a second section having a flexible portion to clamp the head, the first section and the second section being fixed relative to each other, wherein said pressure element is insertable from the opening.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/233,406, filed Aug. 12, 2009, the contents ofwhich are hereby incorporated by reference in their entirety, and claimspriority to European Patent Application EP 09 167 751.8, filed Aug. 12,2009, the contents of which are hereby incorporated by reference intheir entirety.

BACKGROUND

1. Field

The invention relates to a receiving part for receiving a rod forcoupling the rod to a bone anchoring element. The receiving partincludes a receiving part body with a channel for receiving a rod and anaccommodation space for accommodating a head of a bone anchoringelement, and a pressure element for clamping the head. The accommodationspace has an opening at a bottom side for inserting the pressure elementand for inserting the head.

2. Description of Related Art

Various designs of polyaxial bone screws are known wherein a head isclamped from the side to lock a rotational position of the bone screw.

U.S. Pat. No. 5,672,176 describes a bone screw with a receiving partwith a conically shaped seat and a conically shaped pressure elementwhich exerts a pressure onto the head from above and from the side.

U.S. Pat. No. 5,669,911 describes a polyaxial orthopaedic device for usewith a rod implant apparatus. The device includes a screw having acurvate head, a locking collar disposed therearound, and a receivingmember having a linearly tapered socket in which the screw and thecollar are nested. The collar is introduced from the top of thereceiving member. The head of the screw can be inserted from the bottom.

U.S. Pat. No. 6,063,090 relates to a device used to connect alongitudinal support to a pedicle screw by an accommodating head havinga channel to accommodate the longitudinal support. The pedicle screw andthe accommodating head are connected via a conical collate chuck in theaccommodating head and by a spherical head on the pedicle screw. Thedevice allows engagement of the pedicle screw in the accommodating headafter the pedicle screw has been inserted into the bone.

SUMMARY

Embodiments of the invention provide an improved receiving part forreceiving a rod for coupling the rod to a bone anchoring element, and abone anchoring device with such a receiving part, where the embodimentshave fewer parts, a low profile, and provide for improved handlingduring surgery.

Embodiments of the invention provide a receiving part including areceiving part body including a first end and a second end, and having asubstantially U-shaped recess at the first end forming a channel forreceiving a rod, and an accommodation space for accommodating a head ofa bone anchoring element, the accommodation space having an opening atthe second end for introducing the head; and a pressure element arrangedat least partially in the accommodation space, the pressure elementincluding a first section having a second recess for receiving the rod,and a second section having a flexible portion to clamp the head, thefirst section and the second section being fixed relative to each other,wherein said pressure element is insertable from the opening, a boneanchoring device including such a receiving part, and a method of usingsuch a receiving part.

For the receiving part according to an embodiment of the invention, thepressure element has a slim design which allows it to be introduced fromthe bottom into the receiving part body. An internal end stop within thereceiving part body may form an abutment for the pressure element to bepositioned in an insertion position for the head. Therefore, there maybe no additional components for holding the pressure element in theinsertion position.

In some embodiments, the receiving part has a low profile and improvedor maximum stiffness, since a wall thickness of the receiving part bodycan be increased due to the slim design of the pressure element.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparentfrom the description of embodiments using the accompanying drawings. Inthe drawings:

FIG. 1 shows a perspective exploded view of a first embodiment of thebone anchoring device.

FIG. 2 shows a perspective view of the bone anchoring device of FIG. 1in an assembled state.

FIG. 3 shows a cross-sectional view of the bone anchoring device of FIG.1, the section being taken perpendicular to a rod axis.

FIG. 4 shows an enlarged perspective view of a pressure elementaccording to an embodiment of the bone anchoring device.

FIG. 5 shows a cross-sectional view of the pressure element according toFIG. 4.

FIG. 6 shows a side view of the pressure element of FIG. 4.

FIG. 7 shows a bottom view of the pressure element of FIG. 4.

FIGS. 8 a to 8 d show schematic views of design modifications of apressure element and a receiving part body in a locking positionaccording to embodiments of the bone anchoring device.

FIGS. 9 a and 9 b show schematic views of a further design modificationof the pressure element and the receiving portion in a pre-lockingposition and a locking position, respectively, according to anembodiment of the bone anchoring device.

DETAILED DESCRIPTION

As shown in FIGS. 1 and 2, a bone anchoring device according to a firstembodiment includes a bone anchoring element 1 in the form of a bonescrew having a threaded shaft 2 and a head 3, which in this embodimentis a spherical segment-shaped head. The head 3 has a recess 4 forengagement with a screwing-in tool. The bone anchoring device furtherincludes a receiving part body 5 for receiving a rod 6 to connect therod to the bone anchoring element 1. Further, a closure element 7, inthe form of an inner screw or set screw in some embodiments, is providedfor securing the rod 6 in the receiving part body 5. In addition, thebone anchoring device includes a pressure element 8 for locking the head3 in the receiving part body 5.

The receiving part body 5 is now explained with reference to FIGS. 1 to3. The receiving part body 5 includes a first end 5 a and a second end 5b, and an axis of symmetry M passes through the first and the secondend. A bore 9, which is coaxial with the axis of symmetry M, extendsfrom the first end 5 a to the second end 5 b. The bore 9 may have asmallest diameter at, about, or adjacent to its middle section 91 in acenter region of the receiving part body 5. In a first region adjacentto the first end 5 a, the receiving part body 5 has a U-shaped recess10, which may be symmetric with respect to the symmetry axis M. Therecess 10 has a bottom which may be directed towards the second end 5 band provides two free lateral legs 11 a, 11 b extending towards thefirst end 5 a. In the region of the legs 11 a, 11 b an internal thread12 may be provided which may cooperate with the closure element 7, whichin this embodiment is a set screw. A channel formed by the U-shapedrecess 10 is sized so as to receive the rod 6 therein, the rod forconnecting a plurality of bone anchoring devices.

At a second region near the second end 5 b, the receiving part body 5has a narrowing portion 13, which narrows in a direction towards thesecond end 5 b. The narrowing portion 13 provides a seat for the screwhead and the pressure element. The narrowing portion 13 is located at adistance from the second end 5 b to, for example, enable the screw shaft2 to be pivoted in a certain pivot angle range. An opening 14 isprovided at the second end 5 b, the diameter of which may be the same asor larger than the diameter of the narrowing portion 13 in someembodiments. Between the narrowing portion 13 and the middle portion 91of the bore 9, a portion with an inner diameter larger than the diameterof the narrowing portion 13 is provided, which forms a space 15 forallowing the pressure element to expand, as described later. At its sideopposite to the narrowing portion 13, the space 15 connects to themiddle section 91 of the bore 9 having the smaller diameter, therebyproviding a circular shoulder 16.

The middle section 91 of the bore 9 includes a circular projection 17 atits side opposite to the space 15, which can also act as a stop, asdescribed below in more detail.

As can be seen in FIGS. 1 and 3 to 7, a pressure element 8 according toan embodiment of the invention includes a first section 81 which issubstantially cylindrical and has an outer diameter which may beslightly smaller than the inner diameter of the middle section 91 of thebore 9, so that the pressure element 8 is movable in the bore 9. Itfurther has a second section 82, which has a hollow interior 83 which issubstantially spherically-shaped and is sized to clamp the sphericalhead 3 therein. The outer diameter of the first section 81 may be, ascan be seen in FIG. 3, smaller than an outer diameter of the head 3 anda largest outer diameter of the second section 82 is greater than theouter diameter of the cylindrical section 81. A free end of the secondsection 82 provides an opening 84 for introduction of the head 3.Further, the second section 82 may have a plurality of slits 85extending from the edge of the opening 84 through the second section 82to define or form slightly resilient legs 90. The number and thedimension of the slits 85 may be such that the wall of the secondportion is flexible enough to snap onto the head 3 when the head 3 isbeing inserted. The slits 85 can extend into the first cylindricalsection 81 as shown in the figures to enhance flexibility. The outerwall surface of the second section 82 may include a first portion 86which may be spherically-shaped, and a second portion 87 adjacent to theopening 84 which may be tapered or curved or otherwise narrowing towardsthe opening 84. The portion 87 cooperates with the narrowing portion 13of the receiving part body when the head is locked in the receiving partbody.

Further, the pressure element has a coaxial bore 88 for providing accessto the screw head by a tool. The first section 81 may have at its freeend a cylindrically-shaped or cylinder segment-shaped recess 89 forreceiving the rod 6 therein.

The dimensions of the pressure element 8 are such that the pressureelement 8 can be inserted through the opening 14 at the second end 5 bof the receiving part body 5, with the cylindrical first section 81inserted first. When the second section 82 passes through the opening14, it may be compressed due to the flexibility of the second section82, or the legs 90 thereof, which allows the pressure element 8 to befully introduced into the receiving part body 5.

The pressure element 8 can be pushed into the receiving part body 5until an upper edge of the first section 81 abuts against the stop 17provided by the annular projection in the receiving part body 5. Whenthe pressure element is in this position, the flexible second section 82is located in the portion between the middle section 91 of bore 9 andthe narrowing portion 13 of the receiving part body 5. In this position,a free space in the space 15 between the outer wall of the secondsection 82 of the pressure element and the inner wall of the receivingpart body 5 provides room for the flexible second section 82 to expandwhen the head 3 is inserted.

A depth of the cylindrical recess 89 of the pressure element is smallerthan a radius of the rod 6, so that the pressure element can be presseddown by means of screwing-in the inner screw 7, which presses onto therod 6, which in turn presses onto the pressure element 8. The pressureelement 8 is oriented in the receiving part body 5 such that itscylindrical recess 89 is aligned with the U-shaped recess of thereceiving part body 5.

The material of which the components of the bone anchoring device aremade is preferably a body compatible metal, such as stainless steel ortitanium, or a body compatible alloy such as a nickel titanium alloy, inparticular Nitinol. However, body compatible plastic materials, such asmedical-grade polyether ether ketone (PEEK), can also be used.

In use, first, the pressure element 8 is introduced via the bottomopening 14 into the receiving part body 5 until it abuts against stop17. This can be done either by the surgeon, or before so that thereceiving part body is preassembled with the pressure element 8.Thereafter, the head 3 is introduced through the bottom opening andpushes the pressure element 8 upwards against stop 17. This is theinsertion position, which allows the screw head 3 to be introducedthrough the opening 84 into the pressure element 8, thereby widening thehollow interior 83, or the legs 90 respectively, until the pressureelement 8 snaps onto the head 3. This can be done either before screwingthe threaded shaft 2 into the bone, or after having screwed in thethreaded shaft 2 into the bone, to mount the receiving part body 5, withthe pressure element inside, onto the head 3. When the head 3 isinserted, it can still pivot within the pressure element 8 if theflexible section 82 is not compressed. A plurality of bone anchoringdevices may be implanted into the bone(s), for example, in the pediclesof adjacent vertebrae, and the rod 6 may be inserted into the boneanchoring devices, respectively. Angular positions of the receiving partbodies may then be adjusted. Finally, the set screw 7 for each boneanchoring device may be tightened, thereby pressing down the rod 6 ontothe respective pressure elements, which are pressed down until thesecond portion 87 of the outer wall of the second section 82 of eachpressure element engages with the narrowing portion 13 of the respectivereceiving part bodies. In this condition, the head of each boneanchoring device is clamped in an interior of the pressure element, sothat it is locked in a desired angular position.

FIGS. 8 a to 8 d show various designs of the narrowing portion 13 of thereceiving part body 5 and the portion 87 of the pressure element 8 whichengages the narrowing portion 13 according to embodiments of theinvention. FIG. 8 a shows the two portions tapering lineally atsubstantially a same angle. This provides a substantially even pressuredistribution between the second portion 87 of the pressure element 8 andthe narrowing portion 13 of the receiving part body 5. FIG. 8 b and FIG.8 c show two different designs where the respective portions are taperedat different angles. FIG. 8 b shows a main contact area at a bottom ofthe narrowing portion 13, and FIG. 8 c shows a main contact area at atop of the narrowing portion 13. FIG. 8 d shows a tapering secondportion 87 of the pressure element 8 and a rounded portion 13 of thereceiving part body, wherein a curvature of the rounded portion isdirected towards a center of the receiving part body 5. With such aconfiguration, a contact area positioned at the rounded portion can beachieved.

In FIGS. 9 a and 9 b a narrowing portion 13′ of a modified example of areceiving part body 5 has a double spherical radius formed by two curvedportions 13 a, 13 b on top of (i.e., adjacent to) each other, with agroove 13 c therebetween. A curvature of the curved portions aredirected towards the central axis M. Correspondingly, a modifiedpressure element 8′ has at its lower end two invertedly curved portions8 a, 8 b which correspond to the curved portions 13 a, 13 b, with acrest 8 c therebetween, and an outer crest 8 d at an outer yielding edgeof the pressure element 8′.

As shown in FIG. 9 a, when the pressure element 8′ moves downward, itslower most edge 8 d engages in the groove 13 c. In this position thereis a frictional clamping of the head 3, which still allows the head 3 tobe pivoted upon exertion of a force, where this force is greater than aforce needed to pivot the head 3 when the head 3 is introduced in aninsertion position. This may be characterized as a pre-lockingcondition. As shown in FIG. 9 b, by further pressing the pressureelement 8′ downward, the curvatures of the pressure element 8′ engagewith the corresponding curvatures of the narrowing portion 13′ tofinally lock the head 3.

Further modifications of the bone anchoring device are possible. Forexample, in one embodiment the pressure element 8 can have a recesscorresponding to the cylindrical recess 89 described above, which may beU-shaped and provides legs extending above the rod. A dual part closureelement can then be used to separately clamp the head and the rod. Adevice for preventing the pressure element from rotating can be provided(not shown). Such a device can be realised, for example, by crimp boresor by a pin extending from the wall into a recess (not shown) of thepressure element.

Further, in some embodiments, the abutment or stop 17, on which apressure element may abut after it is inserted through the bottomopening and pushed further inwards, can be provided at other locationsin the receiving part, for example, at the circular shoulder 16, whichmay then interact with a corresponding projecting part of the pressureelement to provide an abutment for the pressure element.

While the present invention has been described in connection withcertain exemplary embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments, but is instead intended tocover various modifications and equivalent arrangements included withinthe spirit and scope of the appended claims, and equivalents thereof.

What is claimed is:
 1. A receiving part for receiving a rod for couplingthe rod to a bone anchoring element, the receiving part comprising: areceiving part body having a first end, a second end, an axis extendingthrough the first end and the second end, a substantially U-shapedrecess at the first end forming a channel for receiving the rod, and anaccommodation space for accommodating a head of the bone anchoringelement, the accommodation space having an opening at the second end forintroducing the head; and a pressure element configured to be arrangedat least partially in the accommodation space, the pressure elementcomprising a first section having a second recess for receiving the rod,and a second section having an expandable portion to insert and clampthe head, the pressure element having a slit extending from a free endof the second section and having an opposite end spaced apart from afree end of the first section, wherein the first section and the secondsection are axially connected to one another, wherein the first andsecond sections of the pressure element are insertable through theopening at the second end of the receiving part body toward the firstend of the receiving part body, and wherein the first section of thepressure element is configured to abut against a stop in the receivingpart body to position the expandable portion in the accommodation space.2. The receiving part of claim 1, wherein the first section of thepressure element has a diameter smaller than a diameter of the opening,and the second section of the pressure element has a diameter largerthan the diameter of the opening.
 3. The receiving part of claim 2,wherein the expandable portion is further configured to be compressiblefor insertion through the opening.
 4. The receiving part of claim 1,wherein in an insertion position, the pressure element is positioned inthe receiving part body such that a space between an outer wall of theexpandable portion and an inner wall of the accommodation space providesfor widening of the expandable portion for inserting the head.
 5. Thereceiving part of claim 4, wherein in the insertion position, the stopprevents further movement of the pressure element toward the first end.6. The receiving part of claim 5, wherein the stop comprises an annularprojection inside the receiving part body.
 7. The receiving part ofclaim 1, wherein the receiving part body comprises a narrowing portionnear the opening, the narrowing portion configured to cooperate with acorresponding portion of the pressure element to clamp the head.
 8. Thereceiving part of claim 7, wherein at least one of the narrowing portionof the receiving part body or the corresponding portion of the pressureelement is tapered.
 9. The receiving part of claim 8, wherein both thenarrowing portion of the receiving part body and the correspondingportion of the pressure element are tapered.
 10. The receiving part ofclaim 8, wherein the other one of the narrowing portion of the receivingpart body or the corresponding portion of the pressure element iscurved.
 11. The receiving part of claim 7, wherein the narrowing portionof the receiving part body comprises two adjacent curved portionsforming a groove therebetween, and the corresponding portion of thepressure element comprises two corresponding adjacent curved portionsforming an inner crest therebetween and further comprising an edge crestalong an outer edge of one of the two corresponding adjacent-curvedportions, wherein the edge crest is configured to snap into the groovein a first locking position of the pressure element, and the inner crestis configured to snap into the groove in a second locking position ofthe pressure element.
 12. The receiving part according to claim 1,wherein the pressure element has a plurality of slits extending from thefree end of the second section towards the first section of the pressureelement.
 13. The receiving part according to claim 12, wherein the slitsextend into the first section of the pressure element.
 14. The receivingpart of claim 1, wherein the receiving part body has a bore extendingbetween the first and second ends, the bore including a hollowcylindrically shaped portion, and wherein the accommodation space ispositioned between the opening and the hollow cylindrically shapedportion.
 15. The receiving part of claim 14, wherein the pressureelement includes a substantially cylindrically shaped portion having adiameter corresponding to a diameter of the hollow cylindrically shapedportion, such that the pressure element is moveable along the axis ofthe receiving part body.
 16. The receiving part of claim 14, wherein theaccommodation space has a larger diameter than a diameter of the hollowcylindrically shaped portion.
 17. The receiving part of claim 14,wherein the expandable portion has a diameter larger than a diameter ofthe hollow cylindrically shaped portion.
 18. The receiving part of claim1, further comprising a closure element, wherein the receiving part bodyhas a bore extending between the first and second ends, and a thread atthe first end for engagement with the closure element for fixing the rodin the channel.
 19. The receiving part of claim 1, wherein when thepressure element is in the receiving part body and the second section ofthe pressure element is moved from a first position to a second positioncloser to the second end of the receiving part body, the second sectionis configured to apply a force on the first section of the pressureelement to move the first section closer to the second end of thereceiving part body.
 20. A bone anchoring device comprising: a boneanchoring element comprising a shaft and a head; a receiving part forreceiving a rod for coupling the rod to the bone anchoring element, thereceiving part comprising: a receiving part body having a first end, asecond end, an axis extending through the first end and the second end,a substantially U-shaped recess at the first end forming a channel forreceiving the rod, and an accommodation space for accommodating the headof the bone anchoring element, the accommodation space having an openingat the second end for introducing the head; and a pressure elementconfigured to be arranged at least partially in the accommodation space,the pressure element comprising a first section having a second recessfor receiving the rod, and a second section having an expandable portionto insert and clamp the head, the pressure element having a slitextending from a free end of the second section and having an oppositeend spaced apart from a free end of the first section, wherein the firstsection and the second section are axially connected to one another; anda closure element, wherein the first and second sections of the pressureelement are insertable through the opening at the second end of thereceiving part body toward the first end of the receiving part body, andwherein the first section of the pressure element is configured to abutagainst a stop in the receiving part body to position the expandableportion in the accommodation space.
 21. A method for coupling a rod to abone anchoring element via a receiving part, the receiving partcomprising a receiving part body having a first end, second end, an axisextending through the first end and the second end, a substantiallyU-shaped recess at the first end forming a channel for receiving therod, and an accommodation space for accommodating a head of the boneanchoring element, the accommodation space having an opening at thesecond end for introducing the head, and a pressure element configuredto be arranged at least partially in the accommodation space, thepressure element comprising a first section having a second recess forreceiving the rod, and a second section having an expandable portion toinsert and clamp the head, the pressure element having a slit extendingfrom a free end of the second section and having an opposite end spacedapart from a free end of the first section, wherein the first sectionand the second section are axially connected to one another, the methodcomprising: inserting the first and second sections of the pressureelement through the opening at the second end of the receiving part bodytoward the first end of the receiving part body until the first sectionof the pressure element abuts against a stop in the receiving part bodyto position the expandable portion in the accommodation space;introducing the head through the opening into the pressure element,wherein the expandable portion of the pressure element expands in theaccommodation space to accommodate the head; inserting the rod into thechannel; adjusting an angular position of the receiving part withrespect to the bone anchoring element to be aligned with the rod; andadvancing a closure element in the substantially U-shaped recess towardsthe second end of the receiving part body, the closure element advancingthe rod towards the second end, the rod advancing the pressure elementtowards the second end, wherein the closure element is advanced until itlocks the relative positions of the rod and the bone anchoring elementwith respect to the receiving part.
 22. The method of claim 21, furthercomprising inserting the bone anchoring element into a bone prior tointroducing the head through the opening into the pressure element. 23.The method of claim 21, further comprising inserting the bone anchoring.element into a bone after introducing the head through the opening intothe pressure element.
 24. The method of claim 21, wherein the closureelement is advanced to a pre-locking position prior to locking therelative positions of the rod and the bone anchoring element withrespect to the receiving part, wherein in the pre-locking position, thehead is frictionally clamped in the pressure element such that theangular position of the receiving part with respect to the boneanchoring element can be adjusted upon exertion of a force on the boneanchoring element or the receiving part that is greater than a force foradjusting the angular position of the receiving part with respect to thebone anchoring element prior to advancing the closure element to thepre-locking position.
 25. The method of claim 21, wherein the rod isinserted into the respective channels of a plurality of receiving parts,wherein the rod connects the plurality of receiving parts and acorresponding plurality of bone anchoring elements to one another.